1. Field of the Invention
The present invention relates to a halogenated diarylamine compound and a synthesis method thereof.
2. Description of the Related Art
A display device using a light-emitting element in which an organic compound is used as a light-emitting substance (an organic EL element) has been developed rapidly as a next generation display device because it has advantages such as thinness, lightness in weight, high response speed, low power consumption, and flexibility. Although there have been various obstacles, technique has been improved such that organic EL televisions have become commercially available recently.
In an organic EL element, when voltage is applied between a pair of electrodes with a light-emitting layer provided therebetween, electrons and holes (carriers) injected from the pair of electrodes form a light-emitting substance in an excited state. When the carriers are recombined, the light-emitting substance in the exited state returns to a ground state, and light is emitted. The wavelength of light emitted from a light-emitting substance is peculiar to the light-emitting substance; thus, by using different types of organic compounds as light-emitting substances, light-emitting elements which exhibit a variety of wavelengths, i.e., a variety of colors can be obtained.
In the case of a display device which is expected to display images, such as a display, at least three colors of light, i.e., red, green, and blue are required in order to reproduce full-color images. To achieve this, for example, there are following methods: a method in which a light-emitting element emitting light with a light-emitting spectrum in a wide wavelength and a color filter are combined, a method in which a light-emitting element emitting light with a shorter wavelength than the wavelength of a desired color and a color conversion layer are combined, a method in which a light-emitting element emitting light with a desired wavelength is used. Among those three methods, the final one, i.e., a method in which a desired wavelength is obtained directly is preferable because loss in energy is small if the method is used.
This method in which a desired color is obtained directly is adapted to the organic EL televisions which have become commercially available; however, in addition to that method, a color filter is used in practice, and a micro cavity structure is employed for a light-emitting element in order to improve color purity. Organic EL televisions have got many advantages but are expected to provide high quality images as next generation televisions, and light-emitting elements exhibiting an appropriate emission color are required to live up to the expectation.
As described above, light emitted from a light-emitting substance is peculiar to the light-emitting substance. There are many measures to improve the color purity of organic EL televisions, but it is very difficult to obtain a light-emitting element which exhibits light emission of a favorable color and has other important properties such as lifetime, power consumption. The important properties such as lifetime, power consumption of the light-emitting element are not only dependent on a light-emitting substance, but also greatly dependent on layers other than a light-emitting layer, an element structure, properties and a relationship between a light-emitting substance and a host, or the like. Therefore, many kinds of materials for light-emitting elements are needed for the growth in this field. Accordingly, materials having various molecular structures for light-emitting elements have been proposed (for example, see Patent Document 1).
As a molecular structure of a material for transport of holes, a triarylamine compound is particularly often used. The structure thereof is thought to be electrochemically stable toward holes. Thus, a triarylamine compound is widely used as a hole-injection material, a hole-transport material, a light-emitting material, and a host material.
A triarylamine compound is combined with a variety of substituents, so that a compound which has a variety of properties can be obtained while the compound can maintain the above-mentioned property of a triarylamine compound. Therefore, a compound which is superior in a luminous quantum yield, a carrier-transport property, a carrier-injection property, an oxidation-reduction property, thermal stability, evaporativity, or solubility in a solvent; a compound which can provide a desired emission wavelength can be obtained; or a compound which is stable toward carrier recombination can be obtained.
Accordingly, a triarylamine compound having a desired aryl group and a simple and easy synthesis method thereof have been expected. In addition, a source material by which the synthesis of a triarylamine compound is simplified and a simpler synthesis method of the source material have been desired.